It is known that Ziegler-type catalysts formed by combining an organometallic compound of the metal of Groups IIA, IIB and IIIA of the Periodic Table with a halide of a metal of Groups IVB, VB or VIB of the Periodic Table are useful for the polymerizing of mono-1 olefins at low pressures and low temperatures to form resinous polyolefins. (The Periodic Table referred to herein is published in Deming, General Chemistry (5th edition, Wiley, 1944), and is reprinted in Handbook of Chemistry and Physics, p. 336 (31st edition, Chem. Rubber, 1949).)
In preparing such catalysts, particularly suitable organometallic compounds are the alkyl, especially the lower alkyl compounds of the metals of Groups IIA, IIB and IIIA, such as aluminum, zinc, cadmium and beryllium. Organometallic compounds in which the metal is attached to cycloalkyl radicals of 3 to 7 carbon atoms or aromatic radicals such as phenyl, as well as halogenated compounds such as dialkyl aluminum chlorides are also suitable.
Some of the metal halides useful in preparing the aforementioned catalysts are the liquid or hydrocarbon soluble halides, particularly the chlorides and bromides, of titanium and vanadium, with the titanium and vanadium tetrachlorides and vanadium oxychloride being preferred. Other liquid or hydrocarbon soluble transition metal compounds suitable in preparation of Ziegler-type catalysts and in the practice of the invention as hereafter defined include chlorides, bromides, and alkoxides of titanium and vanadium, and mixed compounds which have the structure EQU MX.sub.n Y.sub.m
where M is titanium, vanadium or vanadyl, and
X and Y are Cl, Br, or OR, and PA1 M + n = valence of M PA1 R is an alkyl containing up to 4 carbon atoms
As specific examples of suitable organometallic compounds used in forming the aforementioned catalysts may be mentioned the dialkyl cadmiums such as diethylcadmium, dimethylcadmium and diisobutylcadmium, the dialkylzincs such as diethylzinc and dibutylzinc, the trialkylaluminums and dialkylaluminum hydrides such as diisobutylaluminum hydride, diethylaluminum hydride, trimethylaluminum, triethylaluminum, tripropylaluminum, triisobutylaluminum and diethylaluminum chloride, the cycloalkyl metal compounds such as tricyclohexylaluminum, and the aryl metal compounds such as diphenylcadmium and dinaphthylzinc. The alkyl group on such compounds is advisably a lower alkyl and particularly such a group having 1 to 4 carbons. It is also known that advantages can be obtained by using the catalysts in association with inert supports or carriers.
A variety of materials have been described in the prior art as effective carriers for the Ziegler catalysts to include a number of magnesium compounds. Among those magnesium compounds listed as carriers in the prior art are magnesium chloride. Although active catalysts are obtained by such magnesium chloride supported Ziegler catalysts in the polymerization of mono-1 olefins, the disadvantage of introducing significant levels of chloride into the polymer, and the variable hydration steps in which magnesium chloride can exist complicate the catalyst preparation procedure and can contribute to poor reproducibility. The disadvantage of employing highly hydrated magnesium compounds such as epsom salts as the catalyst support is that in treating the support excessive amounts of the transition metal compound are consumed by the support before the catalyst can be activated.
In U.S. Pat. No. 2,981,725 there is described a process wherein a water-soluble inorganic salt such as sodium carbonate, potassium carbonate, calcium chloride, sodium chloride, sodium sulfate or magnesium chloride is introduced as an additive to the polymerization mixture containing a transition metal halide, an organometallic compound and ethylene gas in a hydrocarbon solvent. The introduction of magnesium chloride as an additive into the polymerization system was not effective as the polymer yields were exceptionally low.